1. Technical Field
The present invention relates to a method and associated structure for increasing the rate at which chromium is etched when contacted by an acid solution.
2. Related Art
An etching of a chromium volume or chromium layer may be required during fabrication of a multilayer semiconductor structure such as a chip carrier. In some applications, a layer of photoresist covers portions of the chromium volume in order to produce a specified pattern. Further, a portion of the chromium volume must be removed using a chemical etchant, while at the same time leaving areas of the photoresist intact. The chemical etchant must have the property of removing all or part of the chromium volume while not attacking the photoresist. One etchant that meets this requirement is hydrochloric acid (HCl).
Known etching processes utilize a dip tank process for etching chromium from a laminated panel. However, horizontal conveyorized spray processing equipment offers greater throughput and better integration with the rest of the manufacturing operation. Some special needs arise in conveyorized processing. For instance, some laminated panels (i.e., thin ones) need to be set into a carrier fixture for processing. Also, one of the techniques used to increase etch rate in dip processes, the addition of a relatively high concentration of chloride salt, is not practical in a conveyorized spray process because of nozzle clogging and accumulation of salts throughout the apparatus.
A second problem associated with the related art is known as “undercut,” wherein some edges of the layer of photoresist are undermined by the acid solution when the solution is left in contact with the chromium volume for excessively long periods of time required to produce the necessary amount of etching.
Thus there exists the need for a method to enhance the chromium volume etch rate so that the etch rate will keep pace with the remainder of the conveyorized process. There also exists a need for accelerating the chromium etch rate so that the undercutting of photoresist layers is minimized or eliminated by minimizing the total time that the panel spends in contact with the etching solution.